The plasma display panel (PDP) manufacturing process includes a preliminary baking step where a seal frit is applied between two glass substrates which are provided with electrodes, inductive components, fluorescent components and partition walls or other like structures; and a seal-forming process step wherein a seal is formed between the glass substrates through the seal frit.
To explain further, in the preliminary baking process, a seal frit, which is a sealing material consists of a soft glass or other like substance, is applied to one of the glass substrates after which the substrate is subjected to a preliminary baking process in a preliminary baking oven. The other glass substrate is then placed over the seal frit of the previously preliminarily baked substrate, and a clamp or other like fixture is applied to bind the two substrates together to form a glass panel assembly within which the previously noted partition walls and other like structures are sandwiched. In the subsequent sealing process, the glass panel assembly is placed into a sealing oven, and is heated to and maintained at the sealing temperature during the adequate time. The sealing temperature is a temperature higher than that at which the seal frit melts, to form a seal between the glass substrates through the seal frit. After sealing, the glass panel assembly is cooled and subjected to an internal atmosphere evacuation process after which a light emitting gas is injected thereto to form the finished plasma display panel.
Japanese Unexamined Patent Publication Nos. H6-36688 and H11-37660 disclose manufacturing equipment and sealing ovens used to seal the glass panel assembly after the preliminary baking process. Upper and lower heaters, or an inductive heater are used. While the sealing processes described by these document provide for specific temperature control within the oven, there is no specific control of the pressure within the oven and ancillary equipment.
Heating a seal frit results in the emission of impure gas which can have an adverse effect on the performance of a plasma display panel. To prevent the impure gas from invading the glass panel assembly during the sealing process, the seal frit is subjected to preliminary baking, before the sealing process, to remove impure gas from the seal frit.
Although the preliminary baking, which is executed before the sealing process, has the effect of removing impure gas, raising the temperature of the seal frit again to the sealing temperature during the sealing process, and maintaining that temperature for a specific period of time, results in cracked gas and other types of impure gas adhering to the irregular surface and/or porous of the seal frit. This residual impure gas eventually escapes into the area between the glass substrates. Moreover, the problem is not limited to not only the escape of residual impure gas from the seal frit and also the escape of air and gas from other baked materials, such as the partition walls, from the glass panel assembly. If there is a significant volume of impure gas remaining within the glass panel assembly, additional time is required to execute a subsequent gas removal process. Also, the repeated release of impure gas within the completed plasma display panel results in degraded light emission characteristics.